Coupling assembly for coupling a rod to a bone anchoring element, polyaxial bone anchoring device, and modular stabilization device

ABSTRACT

A coupling assembly for coupling a rod to a bone anchoring element, and including a receiving part having a first end, a second end, and an accommodation space having an opening at the second end for inserting a head of the bone anchoring element, a pressure element insertable from the first end, positionable in the accommodation space, and configured to hold the head, the pressure element having at least one spring portion extending circumferentially around the pressure element and being radially compressible, and a rod receiving element separable from the pressure element, wherein in a first position, the spring portion is configured to engage an engagement structure at an inner wall of the receiving part to prevent movement of the pressure element towards the first end, and wherein the rod receiving element is configured to move the pressure element from the first position towards the second end.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.14/490,569, filed Sep. 18, 2014, which claims priority to and thebenefit of U.S. Provisional Patent Application Ser. No. 61/879,916,filed Sep. 19, 2013, the contents of which are hereby incorporated byreference in their entirety, and claims priority from European PatentApplication EP 13 185 176.8, filed Sep. 19, 2013, the contents of whichare hereby incorporated by reference in their entirety.

BACKGROUND Field

The invention relates to a coupling assembly for coupling a rod to abone anchoring element. The coupling assembly includes a receiving partwith a recess for receiving the rod and an accommodation space foraccommodating a head of the bone anchoring element, a pressure elementto clamp the head, and a separate rod receiving element that isconnectable to the pressure element and configured to support the rod.The pressure element has at least one spring portion that extends over alength in a circumferential direction and that is configured to engage aportion of an inner wall of the receiving part so that the pressureelement can be held in a position that prevents an inserted boneanchoring element from being removed. The invention further relates to abottom loading type polyaxial bone anchoring device with such a couplingassembly. Still further, the invention relates to a modular polyaxialbone anchoring device including the coupling assembly and at least twodifferent rod receiving elements that can be used interchangeably withat least two associated closure mechanisms. The invention furtherrelates to a modular stabilization device using the polyaxial boneanchoring device and at least two stabilizations rods having differentdiameters or one rod with at least two sections having differentdiameters.

Description of Related Art

US 2010/0234902 A1 describes a receiving part for receiving a rod forcoupling the rod to a bone anchoring element, the receiving partincluding a receiving part body with a channel for receiving the rod anddefining an accommodation space for accommodating a head of a boneanchoring element and a pressure element at least partially provided inthe accommodation space. In one embodiment the pressure elementcomprises two upstanding resilient fingers with outwardly directedportions at their free ends that can snap below pins extending throughthe wall of the receiving part in order to secure a pre-locking positionof the pressure element in which the head can no longer be removedthrough the bottom end of the receiving part.

US 2010/0160980 A1 describes a locking mechanism and a method offixation of a bone screw and a rod to the spine. The locking mechanismincludes a body, an insert, a rod seat and a set screw. The bodyincludes a bottom portion configured to receive the bone screw and theinsert, but prevents the insert and the bone screw from passingtherethrough once the insert and the bone screw are engaged. The rodseat is between the rod and the insert.

SUMMARY

It is an object of the invention to provide an improved couplingassembly for a bottom loading type polyaxial bone anchoring device, andsuch a polyaxial bone anchoring device, that allows for improved oreasier handling during surgery. Furthermore, it is an object to providea modular polyaxial bone anchoring device and a modular stabilizationdevice that offers a greater variety of applications based on themodularity of the system.

The coupling assembly includes a pressure element that has at least onespring portion extending over a length in a circumferential directionand that is compressible in a radial direction. The spring portion isconfigured to engage an engagement structure at an inner wall of thereceiving part. In a first engagement position, the spring portionengages a first engagement structure at the inner wall of the receivingpart to prevent upward movement of the pressure element in the receivingpart during insertion of the head of the bone anchoring element. In asecond engagement position, the spring portion engages a secondengagement structure at the inner wall of the receiving part in apre-locking position, wherein the bone anchoring element is preventedfrom being pulled out from a lower opening of the receiving part.

In the pre-locking position of the pressure element, the head of thebone anchoring element may be held by a frictional force exerted by thepressure element onto the head. The frictional force may be such thatpivoting of the head is still possible by applying a force thatovercomes the frictional force.

According to an embodiment of the invention, the flexible portion of thepressure element has a circumferentially extending slit forming a slitring or a portion of a slit ring at the bottom end of the pressureelement. The slit ring can expand in a radial direction to allow forinsertion of the head of the bone anchoring element. A force necessaryfor inserting the head into such a flexible portion of the pressureelement is reduced compared to pressure elements that have, for example,a flexible portion with only longitudinal or coaxial slits. Therefore,easier assembly of the polyaxial bone anchoring device is facilitated.

The coupling assembly can be assembled in situ with a bone anchoringelement that has already been inserted into a bone or a vertebra.

In an embodiment, the pressure element may have a recessed portion atits lower end that allows the shank of the bone anchoring element topivot at a larger angle to one side compared to other sides of thepressure element. The pressure element further may have an indicationfeature configured to cooperate with an instrument to indicate theposition of the recessed portion that provides the greater pivot angle.The enlarged pivot angle in one direction may be needed for specialapplications, for example, applications in the cervical spine.

A rod receiving element may have a groove with a shape that allowssupport of rods or rod sections having different diameters. Therefore, amodular stabilization device is provided that includes the boneanchoring device and a variety of rods with different diameter or one ormore rods that have a change in diameter over the length of the rod.This renders the polyaxial bone anchoring device suitable for manydifferent applications that depend on different diameters of the rods tobe used.

In an embodiment, a first type of a rod receiving element has a firstheight in an axial direction that is smaller than the diameter of a rodto be supported. The first type of rod receiving element is configuredto be used, for example, with a single part locking device that locksthe head and the rod simultaneously.

In another embodiment, the rod receiving element has a second height inan axial direction that is greater than the largest diameter of a rod tobe supported. The second type of rod receiving element is configured tobe used, for example, with a two part locking device that locks the headand the rod independently.

A modular polyaxial bone anchoring device includes a bone anchoringelement, the coupling assembly with the first type of rod receivingelement and a single part locking device and the second type of rodreceiving element with a two part locking device. The first type of rodreceiving element with the single part locking device and the second rodreceiving element with the two part locking device can be usedinterchangeably. The assembly of the polyaxial bone anchoring device ismore easily facilitated. Therefore, a kit comprising the modular partscan be provided and part selection and assembly can be made on demand.

The modular polyaxial bone anchoring device furthermore can includeseveral bone anchoring elements that may differ in regards to the lengthof the shank, the anchoring features of the shank, such as differentthread types, thread pitches etc., different diameters of the shank, andin regards to cannulated on non-cannulated shanks.

The modularity in terms of the bone anchoring element and the type ofclosure element to be used, as well as the modularity in terms of therods that can be employed, opens provides for a large variety ofimplants for the surgeon. In addition, the costs for stock-keeping maybe reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will become moreapparent from the description of various embodiments using theaccompanying drawings. In the drawings:

FIG. 1 shows a perspective exploded view of a first embodiment of a boneanchoring device;

FIG. 2 shows a perspective view of the bone anchoring device of FIG. 1in an assembled state;

FIG. 3 shows a cross-sectional view of the bone anchoring deviceaccording to the first embodiment of FIGS. 1 and 2, the cross-sectiontaken perpendicular to an axis of an inserted rod;

FIG. 4 shows a perspective view from above of a receiving part accordingto the first embodiment;

FIG. 5 shows a perspective view from the bottom of the receiving partshown in FIG. 4;

FIG. 6 shows a top view of the receiving part shown in FIGS. 4 and 5;

FIG. 7a shows a cross-sectional view of the receiving part shown inFIGS. 4 to 6 along line A-A in FIG. 6;

FIG. 7b shows an enlarged view of a detail of FIG. 7a ;

FIG. 8 shows a perspective view from above of a pressure elementaccording to a first embodiment;

FIG. 9 shows a perspective view from the bottom of the pressure elementshown in FIG. 8;

FIG. 10 shows a side view of the pressure element shown in FIGS. 8 and9;

FIG. 11 shows a top view of the pressure element shown in FIGS. 8 to 10;

FIG. 12 shows a cross-sectional view of the pressure element of FIGS. 8to 11 along line B-B in FIG. 11;

FIG. 13 shows a perspective view from above of a rod receiving elementaccording to a first embodiment;

FIG. 14 shows a perspective view from the bottom of the rod receivingelement of FIG. 13;

FIG. 15 shows a top view of the rod receiving element shown in FIGS. 13and 14;

FIG. 16 shows a cross-sectional view of the rod receiving element ofFIGS. 13 to 15 along line D-D in FIG. 15;

FIG. 17 shows a cross-sectional view of a first step of assembling thecoupling assembly according to the first embodiment;

FIG. 18a shows a cross-sectional view of a second step of assembling thecoupling assembly according to the first embodiment;

FIG. 18b shows an enlarged cross-sectional view of a detail of FIG. 18a;

FIG. 19 shows a cross-sectional view of a first step of assembling thepolyaxial bone anchoring device (e.g., with a bone anchoring element)according to the first embodiment;

FIG. 20 shows a cross-sectional view of a second step of assembling thepolyaxial bone anchoring device according to the first embodiment;

FIG. 21a shows a cross-sectional view of a third step of assembling thepolyaxial bone anchoring device according to the first embodiment;

FIG. 21b shows an enlarged view of a detail of FIG. 21a ;

FIG. 22 shows a perspective view of a pressure element of a couplingassembly according to a second embodiment;

FIG. 23 shows a side view of the pressure element shown in FIG. 22;

FIG. 24 shows a perspective view from above of a rod receiving elementof a coupling assembly according to a second embodiment;

FIG. 25 shows a perspective view from the bottom of the rod receivingelement shown in FIG. 24;

FIG. 26 shows a top view of the rod receiving element shown in FIGS. 24and 25;

FIG. 27 shows a cross-sectional view of the rod receiving element shownin FIGS. 24 to 26 along line G-G in FIG. 26;

FIG. 28 shows a perspective schematic view of a modular polyaxial boneanchoring device;

FIG. 29a shows a cross-sectional view of the polyaxial bone anchoringdevice according to the first embodiment with an inserted rod having afirst diameter and a single part locking device;

FIG. 29b shows a cross-sectional view of the polyaxial bone anchoringdevice according to the first embodiment with an inserted rod having asecond diameter and a single part locking device;

FIG. 30a shows a cross-sectional view of a polyaxial bone anchoringdevice according to the second embodiment with an inserted rod having afirst diameter and a two part locking device; and

FIG. 30b shows a cross-sectional view of the polyaxial bone anchoringdevice according to the second embodiment with an inserted rod having asecond diameter and a two part locking device.

DETAILED DESCRIPTION

Referring to FIGS. 1 and 2, a bone anchoring device according to a firstembodiment includes a bone anchoring element 1 in the form of a bonescrew having a shank 2 that is at least partially provided with a bonethread, and a head 3. The head 3 has a spherical segment-shaped surfaceportion including a greatest outer diameter E of the sphere and a flatfree end with a recess 4 for engagement with a screwing-in tool.

The bone anchoring device further includes a coupling assembly 5 forreceiving a stabilization rod 100 and for coupling the stabilization rod100 to the bone anchoring element 1. The coupling assembly 5 includes areceiving part 6 for receiving the head 3 of the bone anchoring element1 and for receiving the rod 100, and a pressure element 7 configured tobe arranged in the receiving part 6. The pressure element 7 is utilizedfor locking the head 3 in the receiving part 6. The coupling assemblyfurther includes a rod receiving element 8 that is connectable to thepressure element 7 and that serves for providing support for an insertedrod 100. A pin 9 may be employed for securing a rotational position ofthe rod receiving element 8, so that a support surface for the rod 100is aligned with a recess of the receiving part 6 through which the rod100 extends as further described below.

Further, a locking element 10 in the form of an inner screw is providedfor securing the rod 100 in the receiving part 6 and for exerting aforce via the rod 100 onto the rod receiving element 8 and the pressureelement 7 to lock the head 3 in the receiving part 6. The lockingelement 10 in this embodiment is a single part locking element that isconfigured to lock the head 3 of the bone anchoring element 1 and therod 100 simultaneously.

The receiving part 6 will now be explained with reference to FIGS. 1 to7 b. The receiving part 6 has a first end 6 a that is a top end and anopposite second end 6 b that forms a bottom end, and a central axis ofsymmetry C passing through the first end 6 a and the second end 6 b. Abore 61 is provided that is coaxial with the central axis C. In a firstregion adjacent to the first end 6 a the receiving part 6 has asubstantially U-shaped recess 62 with a bottom directed towards thesecond end 6 b and two free lateral legs 62 a, 62 b extending towardsthe first end 6 a. On the legs 62 a, 62 b, and internal thread 63 isprovided that cooperates with the locking element 10. The channel formedby the U-shaped recess 62 is sized so as to receive the rod 100 thereinfor connecting at least two bone anchoring devices. In the region of thelegs 62 a, 62 b to substantially a height in an axial direction definedby the bottom of the U-shaped recess 62, the bore 61 has a firstdiameter. In a region below the legs 62 a, 62 b, the bore 61 has awidened portion 61 a with a diameter greater than the first diameter ofthe bore 61. Between the second end 6 b and the widened portion 61 a,the bore 61 has a narrowing portion 61 b that tapers and narrows towardsthe second end 6 b with a cone angle. An opening 64 is provided at thesecond end 6 b, the diameter of the opening 64 being larger than thelargest diameter E of the head 3 to allow the insertion of the head 3from the second end 6 b of the receiving part 6. The widened portion 61a and the narrowing portion 61 b define an accommodation space for thehead 3 of the bone anchoring element 1.

Between the portion of the bore 61 with the first diameter that islocated adjacent to the first end 6 a and the widened portion 61 a ofthe bore 61, there is a recess 65 that extends circumferentially at theinner wall of the receiving part 6 and that has a substantially conicalshape widening in a direction from the second end 6 b towards the firstend 6 a. As can be seen in detail in FIGS. 7b , the size of the recess65 is such that, at the end facing the second end 6 b of the receivingpart 6, the recess 65 has an inner diameter corresponding substantiallyto the first diameter of the portion of the bore 61 nearer to the firstend 6 a, and therefore forms an annular inwardly protruding edge 66 atthe upper end of the widened portion 61 a. The protruding edge 66defines a first stop. An upper or opposite end or region of the recess65 has a greater diameter than the portion of the bore 61 nearer to thefirst end 6 a, and forms a second edge 67 that defines a second stop. Acone angle of the recess 65 is such that a spring portion provided atthe pressure element 7 can be held in the recess 65 in a pre-stressedmanner, as further described below.

At at least one of the legs 62 a, 62 b, a transverse bore 68 is providedthat extends through the leg, for example through the leg 62 b, in adirection substantially perpendicular to the central axis C forreceiving the pin 9. The pin 9 has a length such that once the pin 9 isinserted into the transverse bore 68, the pin 9 extends a short distanceinto the bore 61 to provide a stop for securing a rotational position ofthe rod receiving element 8, as further described below. The pin 9 maybe flush with an outer surface of the receiving part 6 when inserted.

Referring to FIGS. 8 to 12, the pressure element 7 has a first end 7 aand a second end 7 b. The second end 7 b of the pressure element 7 isconfigured to be closer to the second end 6 b of the receiving part 6than the first end 7 a of the pressure element 7 is to the second end 6b of the receiving part 6 when the pressure element 7 is arranged in thereceiving part 6. The pressure element 7 is a substantially cap-likepart that has a hollow interior chamber 71 with an opening 72 at thesecond end 7 b, wherein the hollow interior chamber 71 is configured andsized to accommodate and hold the head 3 of the bone anchoring element 1therein. An opening 73 near the first end 7 a that communicates with thehollow interior chamber 71 allows access to the recess 4 of an insertedhead 3 with a tool from the first end 7 a of the pressure element 7. Thelower opening 72 is sized to allow the insertion of the head 3 from thesecond end 7 b. A lower portion 71 a of the pressure element 7 adjacentto the second end 7 b tapers or narrows towards the second end 7 b withan outer surface, which in this embodiment matches or correspondssubstantially to the shape of the narrowing portion 61 b of thereceiving part 6.

At a distance from the second end 7 b, a circumferentially extendingslit 74 is provided. The slit 74 extends around the central axis C ofthe pressure element 7 along a plane substantially perpendicular to thecentral axis C. Further, the slit 74 extends around more than 180°, andpreferably more than 270°, and further preferably more than 340° aroundthe central axis C. By means of the slit 74, a ring-shaped portion atthe second end 7 b is provided that is integrally connected to the restof the pressure element 7 by a wall portion forming a connecting strip75. The connecting strip 75 has a length in the circumferentialdirection such that it provides a stable connection of the ring-shapedportion to the rest of the pressure element 7. At one end of thecircumferentially extending slit 74, there is a substantially verticalslit 76 that extends from the second end 7 b fully through thering-shaped portion into the circumferentially extending slit 74. Bymeans of this, the ring-shaped portion is cut through or split in acircumferential direction and forms a slit ring 77 that can be expandedand compressed in a radial direction. The outer surface of the slit ring77 forms the narrowing outer surface of the lower portion 71 a thatnarrows towards the second end 76 of the pressure element 7. A positionand size of the slit ring 77 is such that when the head 3 of the boneanchoring element 1 is inserted through the opening 72 into the hollowinterior chamber 71, the slit ring 77 expands so that the width of thevertical slit 76 becomes larger, and when the head 3 has been fullyinserted into the hollow interior chamber 71, the slit ring 77encompasses the head 3 at or below a position of the largest diameter Eof the head 3 in a direction towards the shank 2. An inner surface ofthe pressure element 7 in the region of the slit ring 77 may bespherical segment-shaped, with a size that is adapted or corresponds tothe size of the head 3.

A portion 71 b of the pressure element 7 adjacent to the slit ring 77 issubstantially cylindrical with an outer diameter that is smaller than aninner diameter of the widened portion 61 a of the receiving part 6. Acorresponding inner surface of the portion 71 b is substantiallycylindrical with an inner diameter corresponding to or slightly largerthan the largest outer diameter E of the head 3.

The pressure element 7 further has an intermediate portion 71 c thatcontinues from or is connected to the cylindrical portion 71 b. Theintermediate portion 71 c has a conical outer surface that widenstowards the first end 7 a of the pressure element 7. An outermost edge78 of the intermediate portion 71 c that faces the first end 7 aprotrudes outward from the rest of the pressure element 7. The coneangle of the intermediate portion 71 c corresponds substantially to thecone angle of the conical recess 65 of the receiving part 6. An innersurface of the intermediate portion 71 c is cylindrical and has an innerdiameter corresponding to the inner diameter of the cylindrical portion71 b.

Next, an upper cylindrical portion 71 d extends from the intermediateportion 71 c towards the first end 7 a of the pressure element 7. Theupper cylindrical portion 71 d has an outer diameter that may besubstantially the same as the outer diameter of the lower cylindricalportion 71 b and that is in particular slightly smaller than the innerdiameter of the bore 61. The upper cylindrical portion 71 d defines thecoaxial bore 73 and a spherical segment-shaped section 710 that may makeup part of the hollow interior chamber 71 and has a radius adapted tothe spherical segment-shaped head 3 of the bone anchoring element 1.Hence, when the head 3 of the bone anchoring element 1 is inserted intothe hollow interior chamber 71 and tilted, as can be seen, for example,in FIG. 3, the spherical segment-shaped section 710 contacts the surfaceof the head 3.

In the intermediate portion 71 c, two spring portions 79 a, 79 b areprovided. The spring portions 79 a, 79 b are ring segment-shaped andextend around the central axis C around an angle a of approximately 90°,as can be seen in particular in FIG. 11. However, the ringsegment-shaped spring portions 79 a, 79 b can extend around a smaller ora larger angle around the central axis C, depending on the desiredflexibility to be achieved.

The spring portions 79 a, 79 b are formed by slits that extendsubstantially coaxially to the central axis C and slits that extendsubstantially in a circumferential direction around the pressure element7. Referring in particular to FIG. 10, the spring portion 79 a is formedby the following slits. A first vertical slit 791 a extends from thelower cylindrical portion 71 b of the pressure element 7 through theintermediate portion 71 c and to approximately the upper cylindricalportion 71 d in a substantially vertical or coaxial direction withrespect to the central axis C. A second vertical slit 792 a is spacedapart from the first vertical slit 791 a in a circumferential directionand extends from the lower cylindrical portion 71 b of the pressureelement 7 to the intermediate portion 71 c. A first or upper horizontalslit 793 a extends from the first vertical slit 791 a in acircumferential direction a distance around the pressure element 7 thatdefines the angle a of the spring portion around the central axis C. Asecond or lower horizontal slit 794 a extends from the upper end of thesecond vertical slit 792 a in a circumferential direction a distancearound the pressure element 7 that is slightly less than the angle aaround the central axis C. A third vertical slit 795 a connects the endsof the first horizontal slit 793 a and the second horizontal slit 794 aon a side opposite the first and second vertical slits 791 a, 792 a.Widths of the vertical slits 791 a, 792 a, 795 a in a circumferentialdirection may be greater than widths of the horizontal slits 793 a, 794a in an axial direction. Further, the width of the upper horizontal slit793 a may be the same as the width of the lower horizontal slit 794 a.

By the first and second vertical slits 791 a, 792 a, a strip is formedthat connects the ring segment-shaped spring portion 79 a with the restof the pressure element 7. By the third vertical slit 795 a, the ringsegment-shaped spring portion 79 a is provided with a free end in thecircumferential direction.

The second ring segment-shaped spring portion 79 b is formed identicallyto the first spring portion 79 a and has a first vertical slit 791 b, asecond vertical slit 792 b, and a third vertical slit 795 b, as well asa first upper horizontal slit 793 b and a second lower horizontal slit794 b. The ring segment-shaped spring portions 79 a, 79 b are arrangedmirror-symmetrical with respect to a mirror plane that contains thecentral axis C and extends between the first vertical slit 791 a, 791 bof each spring portion, as depicted in particular in FIG. 12. Hence, thefree ends of the ring segment-shaped spring portions 79 a, 79 b pointtowards each other in the circumferential direction.

The spring portions 79 a, 79 b are compressible and expandable in aradial direction. When the pressure element 7 is inserted into the bore61 of the receiving part 6, the spring portions 79 a, 79 b are slightlycompressed so that the pressure element 7 can move downward in the bore61 (i.e., towards the second end 6 b ). Once the spring portions 79 a,79 b have passed the portion of the bore 61 having the first diameter,they are configured to resiliently snap into the conical recess 65.

The pressure element 7 further includes adjacent to the first end 7 a, aplurality of upstanding ring segment-shaped projections 71 e that arespaced apart in a circumferential direction and that are slightlyresilient. An outer surface of the projections 71 e may be slightlytapered so as to provide for a safe connection with the rod receivingelement 8, as further described below. An inner surface of theprojections 71 e may be cylindrical. The upstanding projections 71 e arespaced apart from or recessed from an outer surface of the uppercylindrical portion 71 d, and surround the coaxial bore 73.

Adjacent to the second end 7 b, there is a recessed portion 796 at thelower edge of the pressure element 7 that is formed by the lower edge ofthe slit ring 77. The recessed portion 796 has a shape and size suchthat the shank 2 of the bone anchoring element 1 can abut at a largerpivot angle against the lower edge of the pressure element 7 when boneanchoring element 1 pivots in the direction of the recessed portion 796,as compared to other directions. Therefore, the recessed portion 796provides for an enlarged pivot angle in one direction. As can be seen inFIG. 10, the recessed portion 796 may be aligned approximately at amiddle of one of the spring portions 79 a, 79 b. A second recessedportion 797 is provided at a corresponding circumferential position inthe inner wall of the upper cylindrical portion 71 d. The secondrecessed portion 797 serves for indicating the position of the firstrecessed portion 796, for example, when the pressure element 7 isengaged with a tool (not shown) that includes an engagement portion toengage the second recessed portion 797. Such a tool could have a visualindication on its handle, for example, that shows the user the positionof the second recessed portion 797, and as a consequence thereof, theposition of the first recessed portion 796. Hence, the position of thefirst recessed portion 796 that provides for the enlarged pivot anglecan be identified even if the polyaxial bone anchoring device hasalready been implanted into a bone or a vertebra. The tool can also beused to engage the second recessed portion 797 in a form fit manner, andto rotate the pressure element 7 to adjust the orientation or directionof the first recessed portion 796.

With reference to FIGS. 3 and 13 to 16, the rod receiving element 8 willbe described. The rod receiving element 8 is a substantially hollowcylindrical part having a first end 8 a and an opposite second end 8 b.A groove 81 having a substantially V-shaped cross section with a roundedbottom 81 a extends from the first end 8 a in the direction of thesecond end 8 b, as can be seen in particular in FIGS. 13 and 16. Thegroove 81 defines a longitudinal direction that is parallel to thelongitudinal axis of the rod 100 when the rod 100 is inserted. Thegroove 81 provides a support surface for supporting the rod 100.Referring to FIG. 3, the rod 100 has a circular cross section and issupported in the groove 81 along two contact lines P1, P2, that extendin a direction parallel to the rod axis. Depending on the diameter ofthe rod section that is supported by the groove 81, the contact linesP1, P2 are located more towards the bottom 81 a of the groove 81 for arod with a smaller diameter, or more towards the first end 8 a of thegroove 81 for a rod with a larger diameter, when compared to the rod 100depicted in FIG. 3. Hence, the groove 81 is configured to supportdifferent rods having different diameters or different rod sections of asingle rod that have different diameters.

Adjacent to the second end 8 b, two opposite annular segment-shapedprotrusions 82 a, 82 b are provided that extend towards the central axisC in a radial direction and along a certain length in thecircumferential direction. A height of the annular segment-shapedprotrusions 82 a, 82 b in the axial direction measured from the secondend 8 b corresponds to a height of the upstanding projections 71 e ofthe pressure element 7. Furthermore, an inner surface of the annularsegment-shaped protrusions 82 a, 82 b is slightly tapered and extendscloser to the central axis C towards the second end 8 b, and isconfigured to cooperate with the tapered outer surface of the upstandingprojections 71 e of the pressure element 7. Once the annularsegment-shaped protrusions 82 a, 82 b engage the outer wall of theupstanding projections 71 e of the pressure element 7, the upstandingprojections 71 e are slightly compressed and abut against the annularsegment-shaped protrusions 82 a, 82 b so that the pressure element 7 isconnected to the rod receiving element 8 and held by a frictional force.The location of the center of the annular segment-shaped protrusions 82a, 82 b in a circumferential direction is at substantially 90° withrespect to the bottoms 81 a of the groove 81.

In the outer wall of the rod receiving element 8 on one side of thegroove 81, an elongate recess 83 that extends substantially parallel tothe central axis C is provided. The elongate recess 83 has a closed end84 towards the first end 8 a that serves as an abutment for the pin 9.By the elongate recess 83, a securing element is provided that alsosecures a correct or desired rotational position of the rod receivingelement 8. The elongate recess 83 is open towards the second end 8 b.

In the described embodiment, depth of the groove 81 is smaller than alargest diameter of a rod that can be supported by the rod receivingelement 8. In other words, the first end 8 a will be located below a topsurface of a rod with a largest diameter that can be supported by therod receiving element 8.

An outer diameter of the rod receiving element 8 is only slightlysmaller than an inner diameter of the bore 61 of the receiving part andis preferably flush with an outer diameter of the upper cylindricalportion 71 d of the pressure element 7 when the pressure element 7 andthe rod receiving element 8 are assembled together as shown in FIG. 3.

The bone anchoring device, as a whole or partially, is made of abio-compatible material, such as a bio-compatible metal or a metalalloy, for example titanium, stainless steel, of a nickel titaniumalloy, for example, nitinol, or of bio-compatible plastic materials,such as, for example, polyetheretherketone (PEEK).

Referring to FIG. 17, the coupling assembly 5 is assembled bypre-assembling the pressure element 7 and the rod receiving element 8,such that the upstanding projections 71 e are inserted and held betweenthe annular segment-shaped protrusions 82 a, 82 b of the rod receivingelement 8. The orientation of the pressure element 7 relative to thegroove 81 of the rod receiving element 8 is such that the center of thespring portions 79 a, 79 b may initially be located in a circumferentialdirection at an angle of substantially 90° measured from thelongitudinal axis of the groove 81. The pre-assembled pressure element 7with the rod receiving element 8 is inserted from the first end 6 a ofthe receiving part, with the second end 7 b of the pressure element 7facing in the direction of the second end 6 b of the receiving part 6.During insertion, the spring portions 79 a, 79 b are compressed in aradial direction because the inner diameter of the portion of the bore61 with the first diameter in the receiving part 6 has a smallerdiameter than the outermost edge 78 of the spring portions 79 a, 79 b.

Referring to FIGS. 18a and 18b , as soon as the pressure element 7 is ina position in which the outermost edge 78 of the spring portions 79 a,79 b has reached the conical recess 65 in the receiving part 6, thespring portions 79 a, 79 b snap behind the protrusion 67 that forms theupper edge of the conical recess 65. Thereby, the spring portions 79 a,79 b are configured to radially expand into the conical recess 65.Thereafter, the pin 9 is inserted into the transverse bore 68 until afront face of the pin 9 extends into the elongate recess 83 provided atthe rod receiving element 8. The pin 9 serves for securing the pressureelement 7 and the rod receiving element 8 against inadvertent rotation,so that the U-shaped recess 62 of the receiving part and the groove 81of the rod receiving element 8 remain aligned. In this condition, thecoupling assembly 5 is pre-assembled and can be used for coupling to abone anchoring element 1 and to a rod 100. In the pre-assembledcondition, it is still possible to rotate the pressure element 7 withrespect to the rod receiving element 8, and therefore also with respectto the receiving part 6, so that the orientation of the first recessedportion 796 that defines the direction having the enlarged pivot anglecan be adjusted.

Referring further to FIGS. 19 and 20, the use of the coupling assembly 5together with a bone anchoring element 1 will be explained. As depictedin FIG. 19, first, a suitable bone anchoring element 1 is selected. Thebone anchoring element 1 may be connected to the coupling assembly 5first, and thereafter inserted into a bone part or a vertebra.Alternatively, the bone anchoring element 1 can be placed first into theimplantation site in a patient's body without the coupling assembly 5being connected thereto. As shown in FIG. 19, the head 3 enters thereceiving part 6 through the lower opening 64 and enters the hollowinterior chamber 71 of the pressure element 7 through the open secondend 7 b of the pressure element 7. When the head touches the slit ring77 of the pressure element 7, the pressure element 7 can not move upwardtowards the first end 6 a of the receiving part 6 because the uppersurfaces of the spring portions 79 a, 79 b abut against the upper edge67 of the conical recess 65 that forms the second stop.

As shown in FIG. 20, further insertion of the head 3 upwards into thehollow interior chamber 71 expands the slit ring 77 within the widenedportion 61 a of the bore 61 of the receiving part 6. The head 3 can thenbe completely inserted into the pressure element 7. Because the slitring 77 does note expand at the connection strip 75 the insertion of thehead 3 may not be precisely coaxial with the central axis C, but insteadmay be slightly out of or misaligned with the central axis C. By thefurther insertion of the head 3, the slit ring 77 may be expanded to amaximum extent to allow the head 3 to enter the upper portion of thehollow interior chamber 71 until the head 3 rests in the sphericalsegment-shaped portion of the chamber 71 that is adjacent to the secondend 7 b. Here, the slit ring 77 can elastically contract around the head3 as shown in FIG. 20.

Referring to FIGS. 21a and 21b , pulling the receiving part 6 upwards asillustrated, and/or pressing down the pressure element 7 with aninstrument (not shown) presses the slit ring 77 into the narrowingportion 61 b of the receiving part 6. The conical shape of the recess 65at the inner wall of the receiving part 6 provides an inclined surfacethat allows the spring portions 79 a, 79 b to slide along the inner wallwhen the pressure element 7 is further moved downwards towards secondend 6 b, thereby gradually compressing the spring portions 79 a, 79 bagain until the upper outer edges 78 of the spring portions 79 a, 79 bsnap behind the second inner protrusions 66 in the receiving part 6. Inthis position, the pressure element 7 is again prevented from movingupwards towards the first end 6 a of the receiving part 6 by the firststop provided by the inner protruding edge 66. The head 3 is alreadyclamped by the slit ring 77. Because the slit ring 77 is located betweenthe head 3 and the narrowing portion 61 b of the receiving part 6, theslit ring 77 is prevented from expanding, and so the head 3 is preventedfrom falling out or being pushed out through the lower opening 64. Thisis the pre-locking condition or position.

In clinical use, usually at least two bone anchoring devices areinserted into the bone and the respective receiving parts 6 are aligned.The heads 3 of the bone anchoring elements 1 are held in the respectivepressure elements 7 by a frictional force. Hence, the receiving parts 6can be easily aligned manually, and their angular positions aremaintained by the frictional force between the heads 3 and the pressureelements 7.

Finally, referring to FIG. 3, the rod 100 is inserted into the receivingpart 6. The rod 100 rests on the upper surface of the groove 81 atsubstantially two longitudinal contact areas P1, P2. Then, the lockingelement 10 is screwed between the legs 62 a, 62 b of the receiving part6. Tightening of the locking element 10 advances the locking element 10towards the rod 100 until it contacts an upper surface of the rod 100.The downward force applied by the locking element 10 is transferred fromthe rod 100 to the pressure element 7. Finally, the head 3 and the rod100 are locked relative to the coupling assembly 5. The head 3 can belocked in a specific angular position with respect to the receiving part6.

The bone anchoring element 1 can be pivoted in the direction of therecessed portion 796 at the second end 7 b of the pressure element 7 toa greater angle relative to the receiving part 6 than in an opposite orother directions.

Referring to FIGS. 22 and 23, a second embodiment of the pressureelement will be described. The pressure element 7′ differs only in thatthe spring portions 79 a ′, 79 b ′ do not have a free end. Instead, eachspring portion 79 a ′, 79 b ′, is attached at the respective ends of thering segment-shaped portions via corresponding axially extending stripsthat are formed by two vertical slits 798 a, 799 a, 798 b, 799 b,respectively, wherein slits 798 a, 798 b extend to the first horizontalslit 793 a, 793 b, and slits 799 a, 799 b extend to the secondhorizontal slit 794 a, 794 b, respectively.

A second embodiment of the rod receiving element will be described withreference to FIGS. 24 to 27. Parts and portions that are identical orsimilar to those of the first embodiment have the same referencenumerals, and the descriptions thereof will not be repeated. The rodreceiving element 8′ includes two opposite upstanding legs 86 a, 86 bthat extend upward from the rod supporting groove 81. The upstandinglegs 86 a, 86 b are provided by a substantially rectangular recess 86that is cut into the hollow cylindrical rod receiving element 8′starting from the first end 8 a towards the second end 8 b. Theupstanding legs 86 a, 86 b have a height such that they extend above atop surface of an inserted rod 100 that rests in the rod supportinggroove 81. This renders the rod receiving element 8′ suitable for usewith a two-part locking device 10′ as depicted in FIG. 28.

The two-part locking device 10′ includes an outer locking element 10 aand an inner locking element 10 b. The outer locking element 10 acooperates with the internal thread 63 of the receiving part 6 and isconfigured to abut against the first end 8 a of the rod receivingelement 8′ according to the second embodiment. The inner locking element10 b can be screwed into a threaded hole of the outer locking element 10a and is configured to cooperate with the rod but not with the insertedrod receiving element 8′. When the two-part locking element 10′ is used,the head 3 of the bone anchoring element 1 can be locked by exertingpressure with the outer locking element 10 a only onto the rod receivingelement 8′ according to the second embodiment, and via the pressureelement 7, 7′ onto the head 3, while the rod can be locked independentlyby exerting pressure with the inner locking element 10 b onto itssurface, independently from the locking of the head 3.

FIG. 28 depicts a modular device for stabilizing bones or vertebrae, andincludes a modular polyaxial bone anchoring device and different kindsof stabilization rods 100, 100′ that have different rod diameters. Themodular polyaxial bone anchoring device includes the receiving part 6and an assembly kit including the rod receiving element 8 according tothe first embodiment and the rod receiving element 8′ according to thesecond embodiment that can be used interchangeably together with thepressure element 7, 7′. Corresponding to the first type of couplingassembly utilizing the rod receiving element 8, the single part lockingdevice 10 can be used as part of the modular device, and correspondingto the second type of coupling assembly utilizing the rod receivingelement 8′, the two-part locking device 10′ can be used as part of themodular device. In other embodiments, various other types of lockingdevices that are configured to cooperate with either the rod receivingelement 8 or the rod receiving element 8′ may also be employed.

A modular polyaxial bone anchoring device further includes at least onebone anchoring element 1, preferably a plurality of bone anchoringelements that may differ with respect to the lengths of the shanks,anchoring features of the shanks, such as different thread types, threadpitches, different diameters of the shanks, cannulated or non-cannulatedshanks, or with respect to various other features. Because the polyaxialbone anchoring device is a bottom loading type polyaxial bone anchoringdevice, the assembly of the polyaxial bone anchoring device is easilymade, for example, by the surgeon or any personnel assisting thesurgeon, so that a suitable bone anchoring device can be provided ondemand during or before surgery.

The modular stabilization device may further include at least two rods100, 101 having different diameters and/or at least one rod havingsections with different diameters.

FIGS. 29a to 30b show various combinations of the elements of themodular system depicted in FIG. 28. In FIG. 29a , the first type ofcoupling assembly using the first type of rod receiving element 8 isused together with a rod 100 of a larger diameter and a single partlocking device 10. The locking device 10 exerts pressure onto the rod100 and locks the rod and the head 3 simultaneously. In FIG. 29b , thefirst type of coupling assembly as shown in FIG. 29a is used togetherwith a rod 101 having a smaller diameter than the rod 100 shown in FIG.29a . The single part locking device 10 exerts pressure onto the rod 101with a smaller diameter and simultaneously locks the head 3 and the rod101. The rod 101 with the smaller diameter is safely clamped in the samemanner as the rod 100 with the larger diameter.

In FIG. 30a , the second type of coupling assembly using the second typeor rod receiving element 8′ is used together with the rod 100 having alarger diameter and with a two-part locking device 10′. The outerlocking element 10 a acts on the first end 8 a of the rod receivingelement 8′, which in turn transfers the force onto the pressure element7 and locks the head 3. The rod 100 can still be moved in an axialdirection, and can be locked independently by the inner locking element10 b that exerts pressure onto the rod 100 but not onto the head 3. FIG.30b shows the same situation as in FIG. 30a , with the only differencebeing that the rod 101 having a smaller diameter than the rod 100 shownin FIG. 30a is used. The inner locking element 10 b has to be screweddeeper into the outer locking element 10 a in order to clamp the rod101.

Various other modifications of the embodiments described above may alsobe contemplated. For example, the receiving part is not limited to theexact shape as shown. The recess 62 of the receiving part does not haveto have an exact U-shape. The bore 61 can also have several sectionswith different widths, as long as the enlarged portion 61 a thatprovides space for the expansion of the pressure element is provided.The narrowing portion at the bottom of the receiving part is shown to betapered, but can also be rounded, for example. Also, the externalsurface of the lower portion at the bottom end of the pressure elements7, 7′ can be rounded. Combinations of the surfaces of the receiving partand the pressure element that cooperate to clamp the head can, forexample, be tapered and tapered, tapered and rounded, rounded andtapered, or rounded and rounded, among other configurations.

The embodiments have been described with one single ring segment-shapedsection on the pressure element that clamps the head. However, there maybe more than one ring segment-shaped section to clamp the head in otherembodiments.

Meanwhile, the horizontal and vertical slits in the pressure elementneed not to be exactly horizontal or exactly vertical, and instead, theymay have inclinations or shapes that differ from a straight or acircular shape, in order to achieve different elastic properties.

In other embodiments, the interior hollow chamber of the pressureelement and/or the head of the bone anchoring element can have differentshapes that restrict the pivoting of the bone anchoring element relativeto the receiving part or the pressure element to one single plane, sothat the pivot connection is not polyaxial, but is instead monoplanar.

It is also possible to provide more than one, for example two or three,recessed portions at the second end of the pressure element, for havingmore than one direction that allows for an enlarged pivot angle. Therecessed portion at the second end of the pressure element can also beomitted, so that the pivot angle is the same in all directions.

In addition, all kinds of rods can be used. While rods with a smoothsurface are shown, roughened rods or rods having other structures mayalso be used. The rods may also be rods made of a flexible material, ormay have flexibility through other means.

While a number of different embodiments are disclosed herein, it isappreciated that different components from the different embodiments canbe mixed and matched to produce a variety of still other differentembodiments.

While the present invention has been described in connection withcertain exemplary embodiments, it is to be understood that the inventionis not limited to the disclosed embodiments, but is instead intended tocover various modifications and equivalent arrangements included withinthe spirit and scope of the appended claims, and equivalents thereof.

1. A coupling assembly for coupling a rod to a bone anchoring element,the coupling assembly comprising, a receiving part having a first end, asecond end, and a central axis extending through the first and secondends, a recess at the first end for receiving the rod, and anaccommodation space for accommodating a head of the bone anchoringelement, the accommodation space having an opening at the second end forinserting the head; a pressure element comprising a compressible portiondefining a hollow interior chamber for holding and clamping the head ofthe bone anchoring element therein, and at least one spring portionextending circumferentially around the pressure element and beingradially compressible, wherein the compressible portion is compressibleindependently from movement of the spring portion; and a rod receivingelement separable from the pressure element for supporting the rod;wherein in a first position, the spring portion engages an engagementstructure at an inner wall of the receiving part to prevent movement ofthe pressure element towards the first end of the receiving part, andwherein the rod receiving element is configured to move the pressureelement from the first position towards the second end of the receivingpart.
 2. The coupling assembly of claim 1, wherein the spring portioncomprises at least one circumferentially extending ring segment-shapedportion that is resiliently compressible in a radial direction. 3.(canceled)
 4. The coupling assembly of claim 1, wherein the springportion has a first end and a second end in the circumferentialdirection, and wherein at least the first end or the second end of thespring portion is connected to another portion of the pressure element,while at least part of the spring portion is spaced apart axially fromother portions of the pressure element.
 5. The coupling assembly ofclaim 4, wherein the first end and the second end of the spring portionare both connected to other portions of the pressure element.
 6. Thecoupling assembly of claim 1, wherein the spring portion extends fartherradially from the central axis of the pressure element at a side facingtowards the closer to a first end of the pressure element than at a sidecloser to a second end of the pressure element.
 7. The coupling assemblyof claim 1, wherein two spring portions are provided on the pressureelement and are respectively positioned on a left side and a right sideof the recess for receiving the rod when the pressure element is in thereceiving part.
 8. (canceled)
 9. The coupling assembly of claim 1,wherein the engagement structure comprises is formed by a recess at theinner wall of the receiving part, and wherein of the recess forms anabutment configured to engage an end of the spring portion.
 10. Thecoupling assembly of claim 1, wherein the engagement structure is at aside of the accommodation space that is facing towards positioned closerto the first end of the receiving part.
 11. The coupling assembly ofclaim 1, wherein an end of the pressure element has a recessed portionthat allows pivoting of the bone anchoring element to a greater anglerelative to the receiving part in a radial direction of the recessedportion compared to other radial directions.
 12. A modular stabilizationdevice comprising the coupling assembly of claim 1 and at least tworods, wherein the two rods have different diameters from one another orwherein at least one of the rods has at least two sections withdifferent diameters.
 13. The coupling assembly of claim 1, wherein therod receiving element has a groove for supporting the rod and legs thatextend longitudinally away from other portions of the rod receivingelement on both sides of the groove.
 14. The coupling assembly of claim1, wherein the rod receiving element and the pressure element areconnectable to each other.
 15. A polyaxial bone anchoring devicecomprising the coupling assembly of claim 1 and the bone anchoringelement having a shank for anchoring to a bone and the head.
 16. Amodular polyaxial bone anchoring device comprising; the polyaxial boneanchoring device of claim 15; a second rod receiving element; a singlepart locking device; and a two-part locking device; wherein a first therod receiving element is configured to cooperate with the single partlocking device to simultaneously lock the head and an inserted rodrelative to the receiving part; and wherein the second rod receivingelement is configured to cooperate with the two part locking device toseparately lock the head and an inserted rod.
 17. (canceled)
 18. Thecoupling assembly of claim 11, wherein the pressure element has anindication feature configured to identify a position of the recessedportion.
 19. The coupling assembly of claim 1, wherein the springportion extends uninterruptedly for 90° around the pressure element inthe circumferential direction.
 20. A coupling assembly for coupling arod to a bone anchoring element, the coupling assembly comprising: areceiving part having a first end, a second end, and a central axisextending through the first and second ends, a recess at the first endfor receiving the rod, and an accommodation space for accommodating ahead of the bone anchoring element, the accommodation space having anopening at the second end for inserting the head; a pressure elementhaving a first end, a second end, a central axis extending through thefirst and second ends, a compressible portion defining a hollow interiorchamber with an opening at the second end of the pressure element forinserting and clamping the head of the bone anchoring element therein,and at least one spring portion extending circumferentially around thepressure element and being radially compressible, wherein the pressureelement is insertable from outside the receiving part through the firstend of the receiving part to the accommodation space while the centralaxes of the receiving part and the pressure element are coaxial orparallel; and a rod receiving element separable from the pressureelement for supporting the rod; wherein in a first position, the springportion engages an engagement structure at an inner wall of thereceiving part to prevent movement of the pressure element towards thefirst end of the receiving part, and wherein the rod receiving elementis configured to move the pressure element from the first positiontowards the second end of the receiving part.
 21. The coupling assemblyof claim 20, wherein in the first position, the spring portion extendsfarther radially from the central axis of the pressure element than athird portion of the pressure element positioned axially above thespring portion, and wherein in a second position, the spring portion andthe third portion of the pressure element extend a same distanceradially from the central axis of the pressure element.
 22. A couplingassembly for coupling a rod to a bone anchoring element, the couplingassembly comprising: a receiving part having a first end, a second end,and a central axis extending through the first and second ends, a recessat the first end for receiving the rod, and an accommodation space foraccommodating a head of the bone anchoring element, the accommodationspace having an opening at the second end for inserting the head; apressure element having a first end, a second end, a central axisextending through the first and second ends, a compressible portiondefining a hollow interior chamber with an opening at the second end ofthe pressure element for inserting and clamping the head of the boneanchoring element therein, and at least one radially compressible springportion defined by a first slit and a second slit each formed in thepressure element and extending circumferentially around the pressureelement; and a rod receiving element separable from the pressure elementfor supporting the rod; wherein in a first position, the spring portionengages an engagement structure at an inner wall of the receiving partto prevent movement of the pressure element towards the first end of thereceiving part, and wherein the rod receiving element is configured tomove the pressure element from the first position towards the second endof the receiving part.
 23. The coupling assembly of claim 22, wherein atleast part of the first slit and at least part of the second slit are ata same circumferential position around the central axis of the pressureelement and are spaced apart axially from one another.